Thread rolling machine



Jan 36 1945. A. B. REED 2,367,612

THREAD ROLLING MACHINE Filed Jan. 12, 1945 3 Sheets-Sheet l 3nventorUhtne s A. Bradford Reed Her-bn*t E. Cove 1 Ittorneg Jan. 16, 1945.

A. B. REED THREAD ROLLING MACHINE Filed Jan. 12, 1943 5 Sheets-Sheet. 2

wilhesa Herberi 6. Covey Isnnentor A.Br-adfor-d Reed. I J

' (Ittorneg Jan. 16, 1945.. A. B. REED 2,367,612

THREAD ROLLING MACHINE Filed Jan. 12, 1943 3 Sheets-Sheet 3 X 3nnentorwitness W Herbert 5.. Cove A. Bradfpr'd Reed Cit torneg Patented Jan.16, 1945 UNITED STATES PATENT OFFICE THREAD ROLLING MACHINE ArthurBradford Reed, Worcester, Mass. Application January 12, 1943, Serial No.472,135

14 Claims.

This invention relates to a thread rolling machine and more particularlyto one in which threads are formed by positively rotated andsynchronized cylindrical thread dies.

In a thread rolling machine of the type set forth in my priorapplication Serial No. 444,130 filed May 22, 1942, threads are rolled bymeans of a plurality of positively driven cylindrical dies which areforced inwardly towards the work center by means of toggle arms or camsoperated through a stress ring which is oscillated in a predeterminedcycle by means of a reversible electric motor connected thereto by arack and pinion.

One object of the present invention is to provide adjustable mechanismin a thread rolling machine which will roll threads according to acontrollable and variable cycle of penetration, dwell and release of therolling dies, and particularly to provide such a mechanism which may bereadily changed or adjusted to give a suitable cyclic movement asrequired by different types of metal work blanks to be treated.

A further object of the invention is to provide a variation in thelength of time of the thread rolling operation or the output of themachine and particularly to control the number of contacts between therolling dies and the work piece during the production cycle, regardlessof the frequency of the cycle.

A further object is to provide a machine having a stress ring arrangedto absorb the stresses set up by the rolling operation which is soconstructed that adjustments may be made for rolling threads on workpieces of different diameters without disturbing the matching of the diethreads.

A further object of the invention is to provide a multiple die machineof this general type having a three point supporting and rolling contactbetween the dies and the Work, and wherein two of the contact membersmay be thread rolling dies and the third die serves primarily as asupport to hold the work in proper position and distribute the thrustsof the thread rolling operation.

A further object of the invention is to provide an easily controlledstarting and stopping mechanism which makes it possible to roll a seriesof work pieces in a continuous succession or to roll only a single workpiece.

A further object is to provide a thread rolling machine wherein verysmall pieces of work may be rolled by means of three contactingcylindrical members. Further objects will be apparent in the followingdisclosure.

Referring to the drawings which illustrate preferred embodiments of thisinvention:

Fig. 1 is a vertical section, partly broken away, through the machine;

Fig. 2 is a top plan View of the machine;

Fig. 3 is a top plan view showing a modification arranged for rolling avery small piece of work;

and

Fig. 4 is a top plan view of another modification in which only one dieroll is fed forward positively.

In the embodiment illustrated in Figs. 1 and 2 of the drawings, a workpiece l0 has threads rolled in its surface by means of cylindrical diesH, I2 and I3 which are mounted to be rotated about either parallel ortilted axes in contact with the work piece. The surface of each die rollis provided with single or multiple threads suitably shaped for therolling operation. Each die roll is mounted on an arbor I4 carried bytwo spaced arms l5'and l6 of a supporting yoke ll. The construction ofthis supporting yoke and the associated parts may be as set forth in myprior application. As shown in Fig. 2, the yoke has a verticallyarranged dovetailed groove slidably interfitting with a wedge portion ona pivot block 20. The pivot block has a partial cylindrical convexsurface mating with a similarly shaped concave bearing surface of ablock 22. The yoke l1 and the pivotally connected blocks 20 and 22 formthe two arms of a toggle having a vertical axis, and the parts are soarranged that when the linked arms of the toggle are moved to bringtheir center lines towards a straight line, the die supported thereby ismoved inwardly toward the work center. A pair of guide links 24 haveaxially aligned bearings at their inner ends which pivotally bear onsleeves 25 and 26 (Fig. 1) surrounding the arbor M of each of the dierolls. The other ends of these guide links are pivotally mounted on thereduced end 28 of a stationary post 29 suitably mounted on the frame ofthe machine. The structures of the three sets of die supports, togglesand guides may be made alike or modified as herein described.

In order to operate the toggle, the outer toggle arm or block 22 ismounted for revolving through a short are about the work axis while theinner toggle arm is held by the links 24. That is, the block 22 isadjustably secured on a stress ring assembly comprising the two spacedstress rings 32 and 33 which are carried by an outer supporting ring 34.The ring groove carrying a set of ball bearings 35 which ride in araceway formed in a top ring 36 of the machine frame and are held inplace by a ring 31. When the stress ring assembly is oscillated 34 has a!ball raceway through a short arc, the two arms of the toggle are movedrelative to the center line of the die roll, while the die roll isobliged to travel in an arc required by the link arms 24 which canoscillate only about the fixed center line of the pivot post 28, 29.

A primary feature of this invention resides in so moving the stress ringassembly that the cycle of penetration, dwell and release of the rollingdies relative to the work may be controlled and varied as required bydifferent types of metal. A preferred construction comprises a cam whichis conncted to oscillate the stress ring assembly through a cycle thatis determined by the shape of the cam. This cam of predetermined shapeis mounted for rotation about its axis by means of power drivingmechanism. This cam is suitably supported on a shaft 4| carried by ballbearings 42 mounted on a top plate of the machine. The lower end of thevertical shaft 4| carries a suitable clutch member 45 arranged to meshwith a movable clutch member 43 which is mounted for vertical slidingmovement on the drive shaft 44.

The peripheral face of the cam engages a roller 46 pivotally mountedbetween two swinging arms 41. These two arms 41 are pivoted at theirouter ends to a post 48 fixed on the plate 42. The innerends of the armsconnect through a pin 49 with a short link 50 which is in turn pivotallyconnected by a pin 5| to a block 52 suitably secured,

as by a screw, to the ring 34 of the stress ring assembly. A compressionspring 54 is secured at one end by a link 55 to one of the rock arms 41.The spring is supported by and surrounds a short sleeve 56 telescopingon a guide rod. The sleeve is carried by the rocking link 51 which ispivotally mounted on the top plate of the machine frame. This springtends to hold the cam roller 46 against the cam 40 and to move thestress ring assembly towards the left, as shown in Fig. 2.

Rotation of the cam moves the stress ring to wards the right against thepressure of the spring and at a rate and in accordance with the cycledetermined by the shape of the cam 40. In order to change that cycle, itis merely required to remove the cam 40 and replace it with anothersuitably shaped dam. The strength of the spring is merely enough to movethe die rolls away from the work, while the cam is required to force thedies into the work to roll the thread. By changing the cam, it ispossible to varythe rate of penetration of the die rolls into the work.Some types of steel can be rolled rapidly, while others require a slowpenetration per revolution of the work. Also, the period of dwell,represented by the upper cylindrical portion of the cam of minimumdiameter, can be varied as required for removing and replacing the workpiece. The cam form shown in the drawings provides a rapid infeedingperiod, during which the roller 46 rides up the portion A of the cam andthe die roll is moved up into contact with the work. The part B of thecam may be a spiral of a uniform incline which provides a suitable rateof penetration of the die threads. The cam surface portion C iscylindrical and thus provides a dwell period during which the threadsare finished and their surfaces brought to a smooth burnishedappearance. The part D of the cam causes the die rolls to leave thework. By changing the shapes of any or all of these portions of the camthe penetration cycle may be varied as desired.

A further feature of this invention comprises rotating the die rolls andoscillating the stress ring and the dies carried thereby in differentand predetermined speed ratios. To this end, I provide a driving motor60, which may be a constant speed electric motor of suitableconstruction and a desired rate. This motor 60 is suitably mounted inthe base of the machine and it drives through a v-belt 6! a pulley 62 ona horizontal shaft 63 suitably mounted on the machine framework. Theright hand end of this shaft 63 carries two gears 64 and 65 (Fig. 2).The gear 65 mesheswith a gear of suitable size 66 located thereabove.This gear 66 is on the end of a short horizontal shaft 61 carrying aworm 68 meshing with a worm gear 69 which is on the bottom of the clutchshaft 44. The gear 64 (Fig. 2) meshes with a gear 10 at the frontthereof. That gear 10 is on the end of a long shaft ll (Fig. 1) locatedin front of the shaft 53. This shaft H, which is suitably mountedinbearings, has a Worm 13 on its left hand end meshing with a worm gear14 arranged on a short vertical shaft 15 suitably mounted on theframework. The upper end of the shaft 15 carries a central gear 16 whichmeshes with a cluster of three ars 18 of equal sizes. Each of thesegears 18 (only one of which is shown) is mounted on a short shaft 19suitably carried in bearings and the upper end of each short shaft 19 iskeyed to the bottom member of a universal driving coupling of standardconstruction. The upper half 8| of this coupling is slidably keyed tothe lower half 82 of a second universal coupling, the upper part 83 ofwhich is threaded onto the lower end of the roll die shaft I4.

The sleeve 26 rotates with the coupling member 83 and with the shaft l4.The yoke arm I6 is provided with a suitably shaped bearing for thesleeve. The upper portion of this sleeve 26 is shaped to provide clutchteeth which project into a narrow slot cut out of the lower face of thedie roll, so that the sleeve and the die roll rotate together. Thisclutch transmits the torque directly from the coupling to the sleeve andthence to the die roll so as to prevent strain being imposed 0n theshaft [4.

By rotating the drive gear 16 and the gear cluster, each one of the dierolls H, I2 and I3 is rotated in synchronism at a speed determined bythe sizes of the gears and the motor speeds. Suitable gears may besubstituted for gears 16 and 18 to obtain any desired rotational speedof the dies. The relative speeds of the dies and the cam 40 may bechanged by means of the change gears 64, 65, 66 and 10. These areconveniently mounted in an external pocket 85 in the framework of themachine. Each of these gears is so mounted on its shaft that it may bereadily replaced by other gears of suitable gear ratios so that thespeed of the cam may be thus changed relative to a given speed of thedie rolls, or vice versa. That is, the cam speed may be left unchangedand the die rolls moved faster or slower, or for a given speed of dierolls the rate of penetration caused by the cam may be made faster orslower. It will be appreciated that a suitable change speed mechanismmay be substituted for the change gears and that the latter have beenillustrated to simplify the drawings.

The clutch 43, 45 has been provided in order that the machine may bemade to operate either continuously or intermittently. In order toeffect an intermittent operation, the lower member 43 of the clutchassembly is slidably mounted on the shaft 44 in accordance with standardprocedure and it is thrown into and out of engagement by means of alever 90 having a yoke arm which carries rollers riding in a groove onthe clutch member 43. The lever 90 is centrally mounted on a pivotcarried by a support 93. The right hand end 94 of the yoke lever 90 hasa tension spring 95 secured thereto. The spring is fixed at its otherend and it tends to hold the clutch parts disconnected. Pivoted at 96 onthe fixed support 93 is a pawl 9'! arranged to ride along the under sideof the yoke arm 90 and to connect the clutch when moved towards theleft.

When the pawl is moved to the right, the spring 95 operates to disengagethe clutch. Fixed to this pawl 91 so as to rock it about the pivot 96 isa lever 98 which passes upwardly through the top of the machine where itmay be manually operated.

A small latch 99 suitably pivoted on the machine frame is arranged" tocontact the right hand end 94 of the lever and hold the clutch feetengaged for a continuous operation of the machine. If the latch 99 isheld out of position, the cam may be caused to operate through a singlecycle and then stop. This is effected by means of a knock off cam I00fixed to the vertical shaft 44 which carries the lower clutch member.The knock off cam has a projecting portion so shaped and arranged thatits periphery strikes the lower end of the lever 98 or the pawl 97 andthus moves the pawl towards the right at the same time that the cam 40has finished its cycle of forcing the dies into the work piece and thenremovingthe the outer ring 34 and by means of a pointer H5 secured tothe lower ring and projecting over a scale placed on the top ring.

A further feature of the invention comprises a simple type ofconstruction which serves to secure the two stress rings 32 and 33 in afixed relationship and to hold the toggle block 22 immovable butadjustably positioned thereon. This comprises, as shown particularly inFig. 1, a pair of lugs I20 formed on the outside of each of the toggleblocks 22. A draw bolt I 2I is pivotally connected to the lugs and itpasses outwardly through a hole in a central flange on the outer stressring 34. The draw bolt I2I is adjustably secured in place by means of ascrew I22 threaded into the bolt. An enlarged head on the screw engagesa washer and the latter, is seated against a shoulder within a recessformed in the outer ring 34. Each of the blocks 22 is provided with twoconcave grooves within which are seated short metal strips I24 havingouter vertical faces lying in contact with the inner scroll cam facesH0. The inner faces of these metal strips are convex and slidably fitwithin the grooves in the toggle blocks 22. The strips I24 are looselypositioned and thereby move freely to make proper adjustment so that thetoggle block 22 may be tilted and fit against a high part on one stressring and a lower part on the other. By means of the draw bolt I2I, thetoggle blocks 22 are clamped agains the stress rings through the indiesto the maximum distance fromthe work.

This permits the.spring 95 to disengage the clutch parts and to holdthem out of engagement until the hand lever 98 is again moved toward theright to force the clutch into an operating position. Thus the cam goesthrough a single cycle although the dies rotate continuously in theirsynchronized relationship. This gives the operator opportunity forremoving the work piece l0 and replacing it by a fresh one, after whichthe lever 98 may be thrown to cause the pawl 91 to connect the clutchparts. Since the cam 40 has been stopped on its low point, the cam willthus be in proper position for starting a new cycle and causing the diethreads to roll properly into the work. If the latch 99 is left in itslowermost position, the clutch parts are held engaged and the knock offcam I00 merely moves the pawl 9'! to the right where it stays in aninoperative position.

Each of the stress rings 32 and 33 is provided with three scroll or camfaces I I 0, and the toggle blocks 22 are arranged to be clamped indesired adjusted positions against those scroll faces. If each of theblocks is moved toward the low end of the scroll cam, then the roll diecarried thereby is moved away from the work center. One of the stressrings, such as the upper ring 32, may also be rotated relative to theother ring into a non-symmetrical arrangement so that when the block 22is clamped in place it contacts with a high point on one cam face and alower point on the other and thereby is tilted. This causes a tilting ofthe roll die and thus makes it possible to roll a tapered thread. Thisrelative movement may be effected by means of a small pinion II2, Fig.1, which is suitably mounted in the upper ring 32 and may be rotated bya hand knob II3 projecting therefrom. The pinion meshes with a shortsection of a rack bar II4 fixed on the outer stress ring 34. Thepositions of the two rings may be determined by means of suitable scalemarkings on the top stress ring 32 and termediate adjusting strips I24,and the stress rings 32 and 33 are likewise held immovable relative tothe outer stress rings 34.

The threads of the three die rolls may be brought initially into ahelical alignment so that when the dies are rotated in synchronism inthe same direction the crests of the threads at the points of contactbetween the dies and the work blank remain at all times on a perfecthelix, in which relation the threads of the dies may be considered asbeing in a helical alignment. This initial alignment is accomplished, asdescribed in my prior application, by vertically moving any of the dierolls through a distance suflicient to match the threads. To this endthe toggle yoke I1 is actually made in two parts I I and 20, one beingvertically slidable on the other. The outer end of the member 20 isshaped to provide a partial cylindrical bearing surface which pivotswithin the toggle block 22. The opposite side of this piece has adovetailed portion I29 (Fig. 2) which slidably interfits with a matingslid'eway formed in the outer end of the yoke IT. The yoke may be splitand provided with a cap screw adapted to draw the parts together andthus clamp the two slide portions in a relatively immovable position.The yoke is supported by means of the micrometer head I28. A centralbore formed within the pivot block 20 carries slidably mounted therein arod I30 having a toe on its lower side projecting laterally through aslot in a wall of the dovetailed portion of the pivot member 20. Thistoe interfits with an undercut recess formed in the body of the yoke I!so that the-yoke is supported on the toe. The rod I30 may be adjustedvertically by means of a suitable micrometer screw I3I threaded into arecess in the upper part of the rod, and the upper end of thismicrometer screw carries the dial head I28 which is adapted to be turnedto register with markings on the stationary portion of the block 20.This provides a fine vertical adjustment of the die roll. These partsare so con-v structed and arranged that any vertical adjustment forhelical alignment of the die rolls will not be affected by loosening thedraw bolt HI and again returning it to a clamping position.

A further feature of this invention comprises the modified arrangementshown in Fig. 3 whereby a very small work piece may be rolled by meansof comparatively large dies. In this construction, the stress ringassembly and the roll die mounts and driving mechanism may be made asabove described, but the roll dies themselves are made of differentsizes and in relatively different positions. In the construction ofFigs, 1 and 2, the dies are of the same size and are arranged atapproximately 120 apart relative to radial lines of the work. In theconstruction of Fig. 3, the two dies I40 and MI are made of sufficientlylarge size to accomplish the desired rolling operation. The centers ofthese dies and the work make an angle between 120 and 180 degrees, andpreferably an angle a little less than 180. Two lateral supports mayengage the work at the opposite sides, but I preferably employ only onesupport I42 which is made small enough to enter the comparatively narrowspace between the dies I40 and MI and act as a steadyrest which takesthe thrust of the two main dies I40 and MI. The roll I42 may be a plainfaced cylindrical body which serves merely to take the thrust and holdthe work in place between the dies I40 and MI, but it is preferablyprovided with suitable threads. The diameter of each large die is amultiple of the diameter of the small threaded roll, and the number ofthreads on each is inversely proportional to the size ratio. The twolarge roll dies I40 and HI may be, for example, six times the diameterof the work and the third roll may be approximately equal in size to thework. The small roll I42 may be provided with a thread having a singlestart, while the larger rolls have six threads or six starts. The threerolls are power driven by the above described mechanism but at speedsinversely proportional to their diameters so that the threads properlymatch with the work. That is, the six lead dies have one-sixth of thespeed of the little roll.

It is desirable that the dies have such an angular relationship relativeto the work as to avoid the formation of a non-cylindrical but equaldiameter work piece. To this end, the dies are so located that the anglebetween the centers of any two of the die rolls relative to the work isnot a multiple of the angle between any other two dies and is notdivisible into 360 degrees. For example, the line a passing through thesmall roll I42 and the work center may make an angle of 103 with thecenter line b of the roll die MI and an angle of 113 with the centerline of the roll die I40. Thus the two dies I40 and MI may be disposedalmost diametrically opposite each other and do most of the work, whilethe roll I 42 acts primarily as a steadyrest against the work surface.

A further modification, which will serve for certain non-precisionoperations, is shown in Fig. 4, an accordance with which only one or twoof the die rolls, such as the roll I50, is mounted on a toggle mechanismarranged to force the die toward the work center. The other two dies I5Iand I52 are arranged to be held stationary relative to the work axis. Tothis end, each of the stress rings may be provided with a scroll faceI54 adapted to cooperate with a toggle block I55 and its associatedtoggle arm I56 and the guide link I51 which locate and serve to move thedie roll I50 inwardly toward the work center as the stress ring assemblyis oscillated. One of the other rolls I5I or I52 may be similarlymounted if desired. In the construction illustrated, each is mounted ona plate I60. The latter is pivotally carried on the post ISI suitablysecured on the framework of the machine and constructed similar to thepost 29 above described. Each plate I60 carries a roller I64 pivotallymounted thereon, and each of these rollers engages a cylindrical portionI62 on each of the stress rings. This construction is such that when thestress rings are oscillated, the rollers I64 ride on cylindricalportions of the stress rings and thus do not cause the dies I5I and I52to move inwardly. At the same time the rollers transmit the thrust fromthe thread rolling operation to the stress ring assembly. The other dieI50 is, however, forced inwardly by the toggle mechanism when the stressring is oscillated and thus causes the thread to be rolled in the work.The toggle block I55 may be moved to any desired position on the scrollcam I54 to accommodate different diameters of work.

It is important that a die roll be in the same helical alignment withthe other rolls after adiustment along the scroll face of the stressring. The construction shown in Fig. 1 insures this. The toggle block 22has a projection I10 lying between the two stress rings 32 and 33 andthe upper and lower flat faces of the block are shaped and arranged tofit snugly between the stress rings. The lower stress ring is supportedsolely by a clamp ring I1I which is carried by a bolt I12 threadedtherein. The head of the bolt rests on a second ring I13 which in turnrests on the top stress ring 32. The upper ring 32 rests on a shoulderI14 on the inwardly projecting flange of the outer stress ring 34. Thelower ring 33 does not touch this flange. When the draw bolt I2I isloosened and the toggle block 22 is to be moved along the scroll facesof the stress rings, the bolt I12 is also loosened slightly. When theparts are to be reassembled, the bolt I12 is turned by a wrench appliedto its head. The upper stress ring 32 is positioned by the shoulder I14.Hence, tightening the bolt first draws the upper clamp ring I13 intoplace against ring 32. Then the lower clamp ring I 1| raises the stressring 33 until it strikes the lower face of the projection I10 on thetoggle member 22 and raises it until the upper face of the projectionI10 strikes the under side of stress ring 32. The clamp screw I22 maythen be turned and form a rigid assembly of stress rings and toggle. Thesole support for the assembly is the set of ball bearings 35 and theselocate the upper stress ring correctly. All of the other parts arelocated relative to that upper ring and the supporting shoulder I14 onthe outer ring 34. It is therefore unnecessary to change the setting ofthe dial head I28 when the die rolls are moved to accommodate adifferent size of work piece.

The operation of the machines will be apparent in view of the abovedescription of my inventions. The speeds of the various parts arecoordinated so that the rate of die rotations and the rate ofpenetration are best suited for a given work piece. For a given speed ofthe main drive shaft, the change gear ratio for the die roll shaft maygive a rate of, say, 3 revolutions per second for each die roll. Theother set of change gears and the worm drive may give a cam shaftrotation of approximately 1 revolution per 3 seconds. Assuming the camto be so shaped that about ascacra two thirds of its surface causes thedie to roll the work. then two seconds are consumed e cotively. In thattwo seconds. the three dies with 4 threads or starts on each will make72 starting contacts with the work. Assuming that the depth v of threadis 0.024 inch, this means that the penetration for each contact is onlyabout 0.00033 inch. The cam is preferably shaped to provide a dwell whenthe cam roller rides over the cylindrical surface portion C. Thisresults in the thread being shaped accurately and provided with a smoothor burnished surface. By chang ing the gears, the ratio of die rotationto work penetration may be made as desired.

The various parts of the machine may be made in accordance with thedisclosure in my prior application except as modified by therequirements of this invention. Various modifications will be readilyapparent to one skilled in the art,

and mechanically equivalent parts may be substituted for those hereindescribed. Hence, the above disclosure is to be considered as settingforth the principles of my invention and preferred embodiments thereofand not as imposing limitations on the appended claims.

I claim:

1. A thread rolling machine comprising three rotatable roll diesarranged in helical alignment to roll a thread on a work blank rotatablysupported therebetween and which hold the blank axially immovablerelative to the dies while the thread is being rolled, power mechanismfor rotating the dies positively and in peripheral synchronism, andpower mechanism including a replaceable cam of required shape and a camfollower connected to move all of the rotating dies simultaneouslythrough equal distances towards and from the work axis in apredetermined and variable cycle of approach, penetration and release,said die rotation and cam movement being coordinated and the operatingsurface of the cam being shaped to cause the dies to penetrate the workprogressively during more than one die revolution and to roll the entirethread length simultaneously at a controlled rate.

2. A thread rolling machine comprising three rotatable roll diesmaintained in a substantially equal spacing to roll the entire threadlength on an axially immovable work piece rotatably supportedtherebetween, power mechanism for rotating the dies positively and insynchronism, means for adjusting the separation of the dies andpositioning them in helical alignment for rolling different sizes ofwork pieces, and mechanism including a cam follower and a replaceablecam moved through a definite cycle for forcing all of the diessimultaneously towards the work axis through equal distances, said workand cam movement being coordinated and the operating surface of the cambeing shaped to cause the dies to penetrate the work progressively andgradually in a predetermined cycle of approach during a plurality ofrotations of the work.

3. A thread rolling machine comprising three rotatable roll diesarranged to roll a thread on a work blank rotatably supportedtherebetween and which hold the blank axially immovable relative to thedies while the thread is being rolled, driving mechanism for rotatingthe dies positively and in peripheral synchronism, power drivenmechanism including a cam connected to move all of the diessimultaneously and equally towards the work axis to roll the thread, anda power driven change speed mechanism connected to coordinate the dieand cam movements to provide a predetermined but variable relationshipof rate of die rotation to the rate of penetration of the die into thework, the operative cam surface being shaped to cause the dies topenetrate the entirethread length simultaneously and progressivelyduring a plurality of die revc lutions and in a predetermined cycle ofapproach, penetration and release.

4. A thread rolling machine comprising three rotatable roll diesarranged to roll the entire thread length simultaneously on a work piecerotatably supported therebetween and which hold the blank axiallyimmovable relative to the dies while the thread is being rolled,precision means for tilting each of the dies axially to roll taperedwork or to control the straightness thereof, mechanism connected torotate the dies positively and in synchronism, power mechanism includinga cam and a follower connected to move the dies simultaneously throughequal distances towards the work axis, means for coordinating the ratesof die rotation and work penetration, said cam having its operativesurface shaped to cause the dies to penetrate the work progressivelyduring a plurality of work rotations and in a predetermined cycle ofpenetration, dwell and removal.

5. A thread rolling machine comprising three rotatable roll diesarranged to roll the entire thread length of an axially immovable workpiece rotatably supported therebetween, precision means for tilting thedies axially to roll tapered work or to control the straightnessthereof, mechanism connected to'rotate the dies positively and insynchronism, a replaceable cam driven through a fixed cycle, and a camfollower connected to move all of the dies simultaneously and equallytowards the work axis, said cam having its operative surface shaped tocause the dies to penetrate the work progressively and at a controlledrate during a plurality of work revolutions, and means for varying theratio of the rate of die rotation to the rate of work penetration.

6. A thread rolling machine comprising two die rolls arranged in helicalalignment to roll a thread on an axially immovable work piece rotatablysupported therebetween, the centers of said rolls and the work making anangle between 120 and 180", a steadyrest holding the work positionedbetween the die rolls, the angles formed by the centers of said rollsand rest relative to the work being indivisible in each other and in 360degrees, means for rotating the die rolls positively and in synchronism,means for forcing said rotating die rolls towards the work axis to rollthe entire thread length simultaneously and means for coordinating therates of die rotation and work penetration so that the dies penetratethe work progressively during a plurality of work rotations and in acontrolled cycle of penetration, dwell and release.

7. A thread rolling machine comprising two die rolls arranged to rollsimultaneously the entire thread length on an axially immovable workpiece rotatably supported therebetween, the centers of said rolls andthe work making an angle between 120 and 180, a steadyrest comprising athird roll of smaller diameter than the others which forms therewith athree point support for the work, the angles formed by lines connectingthe axes of said rolls with the work axis being indivisible in eachother and in 360 degrees, means for rotating the rolls in synchronismand at rates inversely proportional to their sizes. means for moving therolls simultaneously to- W ds the work, center and holding the workaxially immovable during the thread rolling operation and means forcontrolling the rates of die rotation and work penetration so that thedies penetrate the work progressively at a controlled rate ofpenetration per work rotation.

8. A thread rolling machine comprising two die rolls arranged to rollsimultaneously the entire thread length on an axially immovable smallwork piece rotatably supported therebetween, the centers of said rollsand the work making an angle between 120 and 180, a third threaded rollof smaller diameter than the others which forms therewith a three pointsupport for the work, the angles formed by the centers of said rollsrelative to the work being indivisible in each other and in 360 degrees,the larger rolls having diameters which are multiples of the diameter ofthe smaller roll and the number of threads thereon being inverselyproportional to the size ratio,

means for rotating the rolls in synchronism and at rates inverselyproportional to their sizes, means for moving said two die rollssimultaneously towards the work center and means for coordinating therates of die rotation and work penetration so that the dies penetratethe work progressively at a controlled rate during a plurality of workrotations.

9. A thread rolling machine comprising three die rolls arranged to rollthe entire thread length on an axially immovable work piece rotatablysupported therebetween, a stress ring having a portion of its innerperiphery lying in a cylindrical surface, means for oscillating thering, means including a die roll support moved by oscillating the ringwhich causes the roll to move towards and from the work center, asupport for another die roll which engages the cylindrical surfaceportion of the ring and transmits thrust without causing the roll tomove, means for rotating the die rolls in synchronism, and means forcoordinating the rates of die rotation and work penetration so that thedies penetrate the work progressively during a plurality of workrotations.

10. A thread rolling machine comprising three die rolls arranged to rollsimultaneously the entire thread length of a work piece rotatablysupported therebetween and which hold the blank axially immovablerelative to the dies while the thread is being rolled, driving mechanismfor rotating the rolls positively and in peripheral synchronism, powermechanism for moving all of the rotating die rolls through equaldistances towards and from the work axis and causing the roll topenetrate the work progressively during a plurality of work rotationsand in a controlled cycle of penetration, dwell and release, a clutchfor controlling said power mechanism, means operated in timedrelationship with the die roll movement tending to disconnect the clutchat the end of a thread rolling cycle, and means for holding the clutchconnected and causing the machine to operate continuously.

11. A thread rolling machine comprising a plurality of rotatable rolldies arranged to roll a thread on an axially immovable work blankrotatably supported therebetween, power mechanism for rotating the diespositively and in synchronism, an oscillatable stress ring. meansoperated by oscillation of the ring which moves the die rollssimultaneously and equally towards and from the work axis, a rotatablecam, a cam tollower operated by the cam and connected to oscillate thering, said cam having an inclined surface which causes the die rolls topenetrate the entire thread length of the work progressively during aplurality of rotations of the work, and power mechanism including achange speed mechanism to rotate the cam in a controlled and variabletimed relation to the die rotation and thereby control the workpenetration per contact of die and work and cause the dies to move in apredetermined cycle of approach, penetration and release relative to thework.

12. A thread rolling machine comprising a plurality of rotatable rolldies arranged to roll a thread on an axially immovable work blankrotatably supported therebetween, an oscillataole stress ring, meansoperated by oscillation of the ring which moves the die rolls throughequal distances towards and from the work axis, means for tiltingthe'dies relative to the work axis, mechanism including a movable camand a follower connected to oscillate the ring in a predetermined cycle,said cam having an inclined surface which causes the dies to penetrateprogressively the entire thread length of the work during a plurality ofwork revolutions, and power driven change speed mechanism connected torotate the dies positively and to move the cam in a predetermined butvariable relationship of rate of die and work rotation to the rate ofwork penetration.

13. A thread rolling machine comprising a casing having an annularsupport, an outer stress ring holder mounted for rotative oscillation onsaid support, two spaced inner stress rings, the upper one of which ismounted on and located by the outer ring, a plurality of thread rollingdies, a support for a die, means for clamping the support and the outerstress ring together and means for adjustably supporting the lower ringon the upper one and clamping it to said support, said die supporthaving upper and lower locating surfaces engaging said inner rings whichaccurately position the die roll relative to a horizontal plane.

14. A thread rolling machine comprising three die rolls arranged to rolla thread on a work piece therebetween, means for rotating the rollspositively and in synchronism, a stress ring having a cam surface and acylindrical surface on its inner periphery, a toggle having one armpositioning a die roll and a second arm adjustably secured to said camsurface, means including a movable support for another die roll having afollower engaging said cylindrical surface which holds the die roll axisin a fixed position as the ring oscillates, said stress ring receivingthe thrusts of the thread rolling operation through said toggle andmovable support, and means for oscillating the stress ring and causingthe toggle to move its associated die roll towards and from the workcenter.

ARTHUR BRADFORD REED.

